The goal of the proposed research is the molecular understanding of light energy transduction, the transport of ions through membranes, and phototaxis. These processes are essential for a molecular understanding of vision, of enzyme catalysis, and of control mechanisms in the cell. The specific aims are the kinetic and structural phenomena that occur in bacteriorhodopsin, halorhodopsin, and sensory and visual pigment rhodopsins. The approach is based on detailed studies of the reaction cycles initiated by light pulses that occur in these pigments as function of temperature, pressure, viscosity, hydration, and extensively and selectively modified chromophores and proteins. Fourier Transform Infrared Difference Spectroscopy of improved signal- to-noise and extended range will be used to detect those vibrational modes in the chromophore and apoprotein that differ in intensity or position between these proteins and their respective intermediates. The kinetics of the relevant change will be followed by using time-resolved Fourier Transform Infrared Difference Spectroscopy, an infrared diode laser system, a fast-rotating wheel, and a flash photolysis system with extended time response. The reactions in all the systems are accompanied by extensive changes in the protein conformation. These conformational changes will be monitored and studied by observations of the relevant IR protein bands, by using pressure jump techniques, and by selectively exciting conformational substrates (hole burning).